The present invention relates to a process for the treatment of complex manganese ores, such as manganiferous nodules found on the ocean bed.
More specifically, it relates to a process making it possible to extract with high yields nickel, copper and cobalt present in manganiferous nodules and to regulate to the desired value the manganese quantity extracted from the treated nodules.
Such manganiferous nodules contain large amounts of manganese and iron, smaller amounts of nickel, cobalt and copper and small quantities of other elements. Nickel, copper and cobalt are high value metals, which are worth extracting from said nodules with higher yields, in view of the fact that there are significant decreases in the known reserves of such metals. Among these, cobalt is particularly difficult to extract by conventional processes in such a way as to give high yields, without simultaneously obtaining a significant solubilization of the manganese.
Thus, according to the process described in French Pat. No. 2,156,079, there is a simultaneous solubilization of manganese, nickel, copper and cobalt by subjecting the nodules to a reduction stage by hot sulphurous anhydride and to a leaching stage by cold sulphuric acid.
In the same way, in U.S. Pat. No. 3,169,856, which describes a process which once again comprise two stages, including a first reduction stage by cold sulphurous anhydride for solubilizing the manganese, nickel and copper and a second stage of leaching the remaining solid phase with an acid in order to recover the cobalt, it is not possible to regulate the manganese quantity dissolved and to have good cobalt yields.
Thus, although manganese is a worthwhile metal, it is not always desirable to recover all the manganese present in the treated nodules.
Thus, numerous studies propose a selective recovery of the nickel and copper, by sulphuric leaching at temperatures below 100.degree. C. In accordance with what has been stated hereinbefore, cobalt is not extracted to any great extent by this process. To obviate this disadvantage, other research has been carried out and would appear to show that in a sulphuric medium, leaching in an autoclave at high pressure and temperature (250.degree. C.) constitutes the only method for the selective solubilization of nickel, copper and cobalt with good yields.
Thus, the objectives of the present invention includes that of providing a novel and improved process for extracting precious metals from complex ores or manganese nodules or any other metal, e.g. containing a manganese oxide matrix.
Another objective is to provide a novel, improved process for extracting cobalt, which may also make it possible to recover nickel and copper elements with excellent yields.
Another objective is to provide a novel process making it possible to selectively extract cobalt, nickel and copper in a sulphuric medium and with good yields, without solubilizing the iron.
Another objective is to provide a novel process making it possible to extract in a sulphuric medium the cobalt, apart from the nickel and copper with good yields and without solubilizing the manganese.
Another objective is to provide a novel process making it possible to extract cobalt, nickel and copper with good yields and without solubilizing the iron, without solubilizing the manganese and without leaching conditions which are as severe as sulphuric leaching in an autoclave at 250.degree. C.
French Pat. No. 2,098,454 has shown that the presence of manganous ions in an ammoniac leaching solution permits an effective solubilization of the nickel and copper. It is also stated that the presence of manganous ions facilitates the recovery of cobalt and molybdenum. It is assumed that in an ammoniac medium, the manganese dioxide is reduced by the manganous ions.
In another French Pat. No. 2,156,079, which relates to the solubilization of nickel, copper, cobalt and manganese contained in nodules, it is stated that during a reducing leaching of nodules by SO.sub.2, the presence of manganous sulphate has a favourable effect on the nickel, copper and cobalt yields.
However, in the latter case, there is a reduction of the manganese of the nodules with solubilization of the said manganese, which constitutes a disadvantage because processes are being sought which do not involve the solubilization of the manganese.
The object of the present invention is a process for the treatment of complex manganese ores, such as manganiferous nodules obtained from the ocean bed and which obviates the said disadvantage.